Electromagnetic electroacoustic transducer



Nov. 26, 1963 R. GORIKE ELECTROMAGNETIC ELECTROACOUSTIC TRANSDUCER FiledNov. 27, 1961 FIG 8 P6 INVENTOR'. RUDOLF GORIHE .BY AGENT M UnitedStates Patent 3,112,374 ELEQTRQMAGNETEQ ELECTROACUUFsTlL TRANDUCERRudolf Giirike, 57c Sternwartestrasse, Vienna XVlll, Austria Filed Nov.27, 1951, Ser. No. 155,167 Qlaims priority, application Austria Nov. 3t1969 16 Claims. (Cl. 179-115) This invention relates to anelectromagnetic electroacoustic transducer which constitutes a ringarmature system. Such ring armature systems distinguish by a concentricarrangement so that they can easily be manufactured.

A ring armature system which has recently been disclosed and has mainlybeen developed as a ring armature earphone for telephone earphone unitscan be considered to represent the present state of the art in thisfield. It consists essentially of an annular pole piece, which defineswith an annular permanent magnet 21 working air gap for the ringarmature. The exciter coil is accommodated inside a U-shaped cavity,which is defined on one side by the annular pole piece and on the otherside by a ring applied to the armature. The permanent magnetic fluxpasses from the cylindrical portion of the magnet through thedisc-shaped portion of the magnet, then through the armature at rightangles thereto and back through the pole piece.

Such a ring armature earphone has special advantages regarding itsefiiciency because it delivers a large sound volume within a widefrequency range and with small non-linear distortions.

The design of other ring armature systems which have been disclosed inthe patent literature is based substantially on the same principle asthe ring armature earphone described hereinbefore. The magnetic systemis always annular and so arranged that the transducer has a centralcavity, which is closed by a diaphragm, which in most cases is slightlycurved. Just as the ring armature earphone described first hereinbefore,the exciting coil is disposed in these systems in a U-shaped grooveformed between the annular pole piece and the annular.

permanent magnet.

Although the acoustic properties of these transducers must generally beconsidered satisfactory, they have disadvantages regarding their designand manufacture. These disadvantages result in increased manufacturingcosts and obstruct a general application of these transducers. Besides,the ring armature system cannot be made as small as desired becausetechnological considerations prevent a manufacture of annular permanentmagnets of relatively complex shape below a certain size.

The invention avoids these disadvantages. It provides a ring armaturesystem which can be manufactured simply and without need forconsiderable adjustments and for expensive special molds for thepermanent magnet so that a transducer embodying the invention can bemade so small that it does not exceed dimensions, e.g., of 4 mm. x 7 mm.and still has a high efficiency.

The electroacoustic transducer according to the invention constitutes aring armature system and is essentialiy characterized in that thepermanent magnet which produces the permanent magnetic flux comprises aplug, e.g. of cylindrical shape, which is disposed at the center of thesystem and is contacted at its two end faces by pole plates thediameters of which are substantially equal, but exceed the diameter ofthe permanent magnet, and at least one external air gap is formed in thefree space between the pole plates, in which air gap the armature havingthe shape of a circular ring (ring armature) of magnetic material isarranged with freedom of vibration, a diaphragm for radiating orreceiving sound fat and consisting preferably of non-magnetic materialis secured and the exciter winding is arranged inside the transducer andconcentric with the axis thereof.

According to another feature of the invention, two air gaps may beprovided, only one of which serves as a working air gap for the ringarmature whereas the other gap disposed inside the transducer isarranged to receive the means for mounting the ring armature. Furtherfeatures of the invention will be apparent from the followingdescription.

FIGS. 1 to 3 and 5 to 7 show various embodiments of the electroacoustictransducer according to the invention. FiG. 4 shows a preferredembodiment of a ring armature used according to the invention and FIG. 8shows by way of example a microphone according to the invention.

As is shown in FIG. 1, the cylindrical permanent magnet 1 forms the coreof the transducer. At each of its two surface-ground end faces, itcarries a pole plate 2, 3, which may consist of a flat plate or may havea different shape, e.g., similar to a pot. Whereas the term plate is notreally appropriate for the last-mentioned plate, it is more desirablefor a clear description to define a comp nent only by its functionirrespective of its shape. For this reason a pot-shaped plate is alsoreferred to as a pole plate, sometimes as a pot-shaped pole plate.

In FIG. 1, the upper pole plate 2 consists of a fiat plate whereas theopposite plate 3 is potshaped. Its upturned rims define with the poleplate 2 an air gap 5, which receives the ring armature f. The diameterof the ring armature slightly exceeds that of the pole plate 2 so thatthe rim of the armature extends beyond the periphery of the drivingsystem. This is necessary because the preferably slightly curved, soundradiating diaphragm 6 of non-magnetic material is secured to the rim,e.g., by being fitted, adhesively connected or flange-connected withapplication of heat. This arrangement has the advantage that more thanthe entire diameter of the transducer is available for a radiation ofsound. This is of decisive significance in the case of small systems. Inthe illustrative embodiment shown in this figure, the excited winding 7concentrically surrounds the cylindrical permanent magnet. The exciterwinding 7 may either be directly wound on the magnet, e.g., withinsulating paper interposed, or it may be wound on a separate coil body.The ring armature 4 is supported at its inside .perimherv at 9 by anon-magnetic sleeve 14-.

The illustrative embodiment according to FIG. 2 difiers from thataccording to FIG. 1 in that two pot-shaped pole plates 3, ltd havingdifferent diameters and arranged one in the other are provided on oneside. This arrangement results in the formation of two air gaps, theouter air gap 5 constituting the working air gap for the ring armature4- whereas the inner air gap 9 serves for securing or mounting the ringarmature 4. In this embodiment the exciter coil is arranged on thecylindrical outside wall of the inner pot-shaped pole plate. Tointensify the magnetic flux through the workingair gap, the upper poleplate 2 is offset at its rim so that the air gap 5 is smaller than theinner air gap 9.

In this connection it may be stated in general that the term air gaprefers also to gaps in which the clearance between the pole faces isfilled by nonmagnetic materials. These nonmagnetic materials serve forretaining the diaphragm.

In order to simplify the manufacture of the transducer according to theinvention, it may be suitable under certain circumstances to use twofiat pole plates 2. and 3 and to mount a pole piece 8 consisting of achannel section bent in the form of a ring on one pole plate 3. Such anembodiment is shown in FIG. 3. The intermediate web portion of thechannelshaped pole piece is in firm engagement with the pole plate 3,and its free ends define with the other pole plate 2 two annular airgaps and the outer one of which serves again as a working air gapwhereas the ring armature 4 is mounted in the inner air gap. Just as thearrangements described hereinbefore, this arrangement comprisesaccording to the invention the cylindrical permanent magnet at thecenter of the transducer. As is shown in FIG. 4, the ring armature usedin all embodiments may have radial slots, which reduce the stiffness ofthe armature and reduce the eddy current losses to some extent. Theslots 11 need not be radial but may be inclined, as is shown in FIG. 4at 13.

FIG. 5 shows an embodiment of the invention comprising two exciter coils7 and 7a. The ring armature 4- is held between two sleeves 14 and 14a ofnonmagnetic material. Two pot-shaped pole plates 2', 3 are symmetricallyarranged and the exciter coil is divided, the two half-windings 7, 7abeing disposed on opposite sides of the ring armature.

FIG. 6 shows an embodiment which comprises also two exciter coils 7 and7a but two air gaps 5 and 9, the gap 5 constituting a working air gapwhereas the inner air gap 9 accommodates the ring armature 4.

For this purpose, at least one of the pole plates 2, 3 is formed at itsrim with a channel section. The free space around the permanent magnetmay communicate through bores 30 with the air cushion behind thediaphragm and with the outside air or a larger air chamber.

FIG. 7 shows another embodiment of the means for mounting the armature.The pole plate 3 is formed at its rim with a channel section, whichaccommodates the exciter winding. The ring armature 4 is mounted betweena cylindrical sleeve 14 and a ring 14a, both of which consist ofnonmagnetic material.

The ring armature need not be of uniform thickness but may be enlargedin certain zones, e.g. in the region of the alternating magnetic flux.This may be effected by the application of a second ring having a largerinside diameter to the gripped thinner ring. These two rings may beconnected by spot welding. Alternatively, a covering of magneticmaterial in the form of a circular ring may be applied to the thinnerarmature ring, e.g., by means of an adhesive.

FIG. 8 shows an illustrative embodiment of a microphone according to theinvention. The magnet 1 has a bore, through which a hollow rivet 15extends, which serves for the fixation of the pole plates 2 and 3. Thediaphragm 6 is provided with a rim zone 16, which is of conical orsimilar shape and which terminates in elastic corrugations 17. Thediaphragm is mounted on the housing 19 at 18. To modify the vibrationsof the diaphragm in a manner known per se, a curved member 213 and amember 21 are provided to define a low air chamber behind the diaphragm.The sound waves can enter the large chamber 26 of the housing 19 throughthe hollow rivet 15, which may accommodate clamping means 22 and 23, andthrough openings 24 in the member 21. The openings 24 may also becovered with damping means 25. A tube 27 extends in a manner known perse in the chamber 26 and leads at 23 into the free sound field. A guardscreen 29 is disposed before the diaphragm. When the sound transducer isinserted in a housing, e.g., a telephone receiver, the pole plates maysuitably be formed with openings 3%), as is shown in FIG. 6. This willreduce the restoring force of the small air chambers behind thediaphragm and will utilize the hollow space of the housing.

Through these openings the rear side of the diaphragm may be exposed tothe external sound field so that a transducer for a directionalreception or radiation of sound is provided.

This is not the only application of the transducer according to theinvention. The same can be manufactured in any size, c.g., in miniaturesize for hearing aids or in a size suitable for incorporation intelephone handsets. The large diameter of the diaphragm will ensure toan excellent acoustic efiiciency as well as an excellent frequencyresponse with minimum distortions whereas the manufacturing costs aremuch less than those of the previously usual transducers.

The invention is not restricted in its application to electroacoustictransducers but may be used, e.g., as a receiver or transmitter forvibrations if the ring armature protruding from the magnetic system isconnected to the inert mass of the vibration-receiving means or to thecoupling means provided for the transmission of force.

Similarly, the invention may be applied to all devices in which adriving force in a circular distribution is provided.

What is claimed is:

1. An electromagnetic electroacoustic transducer, which comprises acentral plug of permanent-magnetic material generating a permanentmagnetic flux and having two mutually opposite end faces, pole meanscomprising two pole plates, each of which contacts one of said end facesand the diameters of which are substantially equal to them selves andlarger than the diameter of said plug, said pole plates defining betweenthemselves a free space, said pole means defining an outer air gap andan inner air gap, an armature of magnetic material in the shape of acircular ring extending through said outer air gap with freedom ofvibration therein and having an inner rim disposed in said inner airgap, said transducer comprising further annular armature retaining meansof nonmagnetic material engaging said inner rim of said armature on bothsides thereof in said inner air gap to retain said armature, saidarmature having an outer rim disposed radially outwardly of theperiphery of said pole means, said transducer comprising further adiaphragm secured to said outer rim of said armature and adapted tovibrate at sound frequencies, and an exciter winding which is disposedin the interior of said transducer and concentric with the axis thereofand adapted to generate an alternating magnetic flux permeating saidarmature where it extends through said outer air gap.

2. A transducer as set forth in claim 1, in which said plug iscylindrical.

3. A transducer as set forth in claim 1, in which said diaphragmconsists of nonmagnetic material.

4. A transducer as set forth in claim 1, in which said armature isformed with slots.

5. A transducer as set forth in claim 1, in which said pole meanscomprise a channel-shaped pole piece which concentrically surrounds saidplug and has a web directly secured to one of said pole plates and twofree edges defining said outer and inner air gaps, respectively.

6. A transducer as set forth in claim 5, in which the other of said poleplates is substantially fiat and has an orTset marginal zone definingsaid outer air gap.

7. A transducer as set forth in claim 5, in which said exciter windingis disposed inside said channel-shaped pole piece.

8. A transducer as set forth in claim 5, in which the interior of saidchannel-shaped pole piece is entirely occupied by said exciter winding.

9. A transducer as set forth in claim 1, in which said pole platescomprise a fiat pole plate and two pot-shaped pole plates havingdifferent diameters and arranged one in the other, said pot-shaped poleplates defining with said flat pole plate said outer and inner air gaps.

10. A transducer as set forth in claim 9, in which said two pot-shapedpole plates define between them a free space containing said exciterwinding.

11. A transducer as set forth in claim 10, in which said two pot-shapedpole plates comprise an inner pole plate having a cylindrical outsidesurface, on which said exciter winding is mounted.

:12. A transducer as set forth in claim 1, in which at least one of saidpole plates has a rim formed with a channel section defining said airgaps.

13. A transducer as set forth in claim 12, which comprises meansdefining'an air cushion with the rear side of said diaphragm and meansconfining with said plug a free space surrounding said plug, saidlast-mentioned means being formed with bores establishing acommunication from said space to said air cushion and the outside air.

14. A transducer as set forth in claim 12, which oomprises meansdefining an air cushion with the rear side of said diaphragm, meansconfining with said plug a free space surrounding said plug, saidlast-mentioned means being formed with bores, and means defining an airchamber larger than said free space around said plug, said boresestablishing a communication from said free space around said plug tosaid air cushion and to said air chamber.

15. A transducer as set forth in claim 12, in which said plug and polemeans are symmetric with respect to a plane, in which said armatureextends.

16. A transducer as set forth in claim 12, in which said channel sectioncontains sa-id exciter winding and in which said armature retainingmeans comprises a cylindrical sleeve and a ring, both of which surroundsaid plug and retain said armature between them.

References Cited in the file of this patent UNITED STATES PATENTS1,822,095 High Sept. 8, 1931

1. AN ELECTROMAGNETIC ELECTROACOUSTIC TRANSDUCER, WHICH COMPRISES ACENTRAL PLUG OF PERMANENT-MAGNETIC MATERIAL GENERATING A PERMANENTMAGNETIC FLUX AND HAVING TWO MUTUALLY OPPOSITE END FACES, POLE MEANSCOMPRISING TWO POLE PLATES, EACH OF WHICH CONTACTS ONE OF SAID END FACESAND THE DIAMETERS OF WHICH ARE SUBSTANTIALLY EQUAL TO THEMSELVES ANDLARGER THAN THE DIAMETER OF SAID PLUG, SAID POLE PLATES DEFINING BETWEENTHEMSELVES A FREE SPACE, SAID POLE MEANS DEFINING AN OUTER AIR GAP ANDAN INNER AIR GAP, AN ARMATURE OF MAGNETIC MATERIAL IN THE SHAPE OF ACIRCULAR RING EXTENDING THROUGH SAID OUTER AIR GAP WITH FREEDOM OFVIBRATION THEREIN ADN HAVING AN INER RIM DISPOSED IN SAID INNER AIR GAP,SAID TRANSDUCER COMPRISING FURTHER ANNULAR ARMATURE RETAINING MEANS OFNONMAGNETIC MATERIAL ENGAGING SAID INNER RIM OF SAID ARMATURE ON BOTHSIDES THEREOF IN SAID INNER AIR GAP TO RETAIN SAID ARMATURE, SAIDARMATURE HAVING AN OUTER RIM DISPOSED RADIALLY OUTWARDLY OF THEPERIPHERY OF SAID POLE MEANS, SAID TRANSDUCER COMPRISING FURTHER ADIAPHRAGM SECURED TO SAID OUTER RIM OF SAID ARMATURE AND ADAPTED TOVIBRATE AT SOUND FREQUENCIES, AND AN EXCITER WINDING WHICH IS DISPOSEDIN THE INTERIOR OF SAID TRANSDUCER AND CONCENTRIC WITH THE AXIS THEREOFAND ADAPTED TO GENERATE AN ALTERNATING MAGNETIC FLUX PERMEATING SAIDARMATURE WHERE IT EXTENDS THROUGH SAID OUTER AIR GAP.